Honeycomb has long been known for use in structural elements where a combination of lightness and strength are desirable. The use of nonmetallic materials such as ceramics and plastics offers additional advantages in terms of processing characteristics and the appearance and properties of the final product.
Thermoset plastics have been used in the manufacture of honeycomb, including honeycomb formed by bonding together corrugated ribbons of the plastic as well as honeycomb formed by bonding together corrugated ribbons of fabric impregnated with thermosetting resin followed by curing the resin in the honeycomb. Honeycomb structures formed with thermoset plastics have certain disadvantages, however, and these include limitations on the manufacturing techniques and a low resistance to damage. Because of the low damage resistance, the product is highly susceptible to damage during fabrication and lay-up and to fragmentation upon handling.
Additionally, structural honeycomb materials for high temperature applications (&gt;500.degree. F.) have not been successfully commercialized to date. This is due in part to difficulties in obtaining concurrently, processability and high temperature durability, in a polyimide matrix.
Polyimide film honeycomb materials have been described (see U.S. Pat. No. 4,921,745, the disclosure of which is incorporated herein by reference). However, these materials are not suitable for structural use.
What is needed in the an are new fiber-reinforced honeycomb structures which can be used in high temperature applications, including aerospace structures, turbine engine structures and heat exchangers.